SynopsisThe concentration of conjugated polyene sequences was studied in y-irradiated PVC with 4% admixture of four epoxy stabilizers: diglycidyl ether of 2,2-bis(4-hydroxy-3-methylphenyl)propane (I), styrene oxide (1,2-epoxy ethyl benzene) (IV), epoxidized ricinus oil (VI), and epoxidized soybean oil (Drapex 6.8) (VII). As in the former investigations (Papers I and II), the process of the formation of the polyenes occurs in two stages. The concentration of polyene sequences with n double bonds, H , the total amount of polyene sequences, ZH,, the average length of the polyene sequence, Fi, and the two extents of reaction Y and p , were computed. The stabilizing effect of all compounds used agrees with the increasing content of epoxy groups. The addition of stabilizers diminishes the value of Fi. The decrease of the fraction of long sequences and the increase of short ones occurs. Apart from the binding of evolved HCl, the protective effect towards the macromolecules of PVC consists mainly in the inhibition of growth of chain dehydrochlorination by the epoxy groups.

SynopsisThe G H C~ values of y-irradiated PVC mixtures and the changes of the epoxy group concentration were studied after addition of various amounts of five epoxy stabilizers: diglycidyl ether of 2,2-bis(4-hydroxy-3-methyl pheny1)propane (I), diglycidyl ether of 2,2-bis(4-hydroxy-3-nitrophenyl)-propane (II), styrene oxide (1,2-epoxy ethyl benzene) (IV), epoxidized ricinus oil (VI), and epoxidized soybean oil (Drapex 6.8.) (VII). It is stated that only about 50% of epoxy groups, declining in the system, take part in binding of HC1; the rest of these groups disappear as a consequence of other reactions. In connection with the data of the previous paper,' the results presented indicate that the process of stabilization goes in two stages. In the first stage the process consists of the HCI capture by the epoxy groups; in the second stage, due to the remaining part of the stabilizer molecule, a protective effect occurs. This effect consists, for the stabilizers I, 11, IV, of gaining the energy by the benzene ring and, for the stabilizers VI, VII, of a mechanical drawing of polymer chains, which makes the energy transfer more difficult. Having the greatest content of epoxy oxygen (about lo%), the styrene oxide (IV) stabilizes best.

Measurements of mechanical resistance and of some chemical changes were performed for a y-irradiated PA 6 polyamide fibre in the form of surgical threads. A relatively high radiation durability was established for irradiation doses of the order of lo' Gy. The sterilizing dose was assumed to be 3 lo' Gy. It was argued that in this dose range a deterioration of the mechanical properties of about 5% should be expected. ZUSAMMENFASSUNG:Die Anderungen der ReiDfestigkeit und einiger chemischer Eigenschaften von PA 6-Fasern in Form von chirurgischen Zwirnen unter dem EinfluR von Gamma-Strahlung wurden untersucht. Fur den Dosisbereich von lo' Gy wurde eine relativ groDe Strahlungsstabilitat festgestellt. Bei der Dosis von 3 . lo' Gy ist eine Verschlechterung der mechanischen Eigenschaften von ungefahr 5 TO zu erwarten.